Noticing faster RH sensor drift than spec on our HOBO MX1101s and a pair of Vaisala HMP7 probes — up to 3–4% off after six months against 33% MgCl2 at 21 C. Do you all stick to annual third-party calibration, or are you comfortable with in-house two-point (33/75%) and swapping sintered filters as routine maintenance? Wondering if the woodshop 30 m down the hall is contributing despite HEPA prefilters changed quarterly.
Enable HMP7 chemical purge weekly; ‘woodshop 30 m’ VOCs accelerate drift — verify at 75% NaCl?
I’d add a third check at 11% LiCl and let each point fully equilibrate overnight in sealed jars; mid-point drift at “33% MgCl2” alone can hide nonlinearity. If the HMP7s recover after a 24–48 h dry soak (0% with fresh desiccant) plus a fresh PTFE/sintered cap, that points to woodshop cologne (VOCs) more than true sensor aging — an activated carbon prefilter near the intake can help. Do you see the same offset at 75% once you stabilize at 21 ±0.2 °C for a few hours?